The invention relates to a displacement machine for compressible media with two spiral feed chambers which are arranged opposite each other in a fixed housing, and with spiral displacement bodies engaging in these feed chambers, consisting essentially of a central disk and of spiral strips which are attached to each side of the disk and which are held in an eccentric manner in relation to the housing, so that during operation each point on the displacement body executes a circular or elliptical movement, depending on the configuration of the guiding device, said movement being limited by the cylinder walls of the feed chamber, and so that the curvature of the strips is dimensioned such that they almost touch the inner cylinder walls and the outer cylinder walls of the feed chamber on in each case at least one sealing line per strip, said sealing line advancing continuously during operation, and, in order to guide the displacement body in relation to the housing, an eccentric arrangement is provided which essentially consists of a drive shaft and of an eccentric disk arranged thereon.
Displacement machines of the spiral structure variety are known for example from DE-C-26 03 462. Machines of this type of structure are used chiefly as compressors for gaseous media. During machine operation, a plurality of approximately sickle-shaped working chambers are enclosed along a displacement chamber between the spiral-shaped displacement body and the two cylinder walls, which working chambers move through the displacement chamber from an inlet to an outlet, their volume continuously decreasing and the pressure of the working substance correspondingly increasing.
A machine of the abovementioned type, in which the spirals encompass a total angle of wrap of 360xc2x0 or more, is known from DE 35 14230 A1. In such a machine, the spiral strips are arranged axially projecting from both sides of a disk which has a hub for supporting the eccentric crank mechanism. Moreover, the arrangement of the spiral strips is such that, during the rotating movement of the disk, the working chambers created on both sides of the disk decrease in volume and compression of the working substance takes place. In general, the strips are arranged symmetrically with respect to the disk.
For working processes which are intended to be carried out at a higher pressure than the surrounding pressure and in which only a slight pressure loss occurs in the process itself, expansion machines are also used in addition to the compression machines for the purpose of exploiting the residual pressure difference, and this improves the overall degree of efficiency of the machines. Working processes which preferably operate at a higher pressure than the surrounding atmospheric pressure, and in which a relatively small drop in pressure occurs in the process, are, for example, fuel cell processes. Such processes are run using commercially available compression and expansion machines in order to maintain the high degree of efficiency of the oxidation of hydrogen in the fuel cell.
It is an object of the invention to configure a machine of the type mentioned at the outset in such a way that the working medium can be both compressed and expanded using just one displacement body revolving in a housing.
According to the invention, this object is achieved by the fact that one feed chamber is configured for compressing the working substance and the other opposite feed chamber for expanding said working substance, the feed chambers and the strips engaging in them consisting essentially of successive circular arc segments, the radii of the circular segments in the compression-side feed chambers and strips essentially decreasing in size, when viewed in a direction of rotation, and the radii of the circular arc segments in the expansion-side feed chambers and strips essentially increasing in size, when viewed in the same direction of rotation.
The spiral strips attached to both sides of the central disk of the displacement body are accordingly designed such that, in the displacement movement of the displacement body advancing during machine operation, the volume of the working chamber enclosed by these strips and by the associated feed chamber decreases on one side of the disk. On the other side of the disk, the volume of the working chamber enclosed by these strips and by the associated feed chamber increases. Compared with the solutions known from the prior art, the spiral strips attached to both sides of the central disk of the displacement body are in this case arranged asymmetrically in relation to each other.
The advantage of the invention is, among other things, that a very simple and therefore cost-effective construction of the machine can be achieved, since both the compression and the expansion take place using just one movable displacement element.
The compression-side feed chamber in general extends from a radially outward low-pressure inlet to a radially inward high-pressure outlet. If the expansion-side feed chamber now extends from a radially inward high-pressure chamber to a radially outward low-pressure outlet, the working substance on the compression side, when viewed in the radial direction, is fed counter to the direction of the working substance on the expansion side. This has the advantage that the stresses on the central disk and on the spiral strips caused by the gas pressures are approximately symmetrical on compression side and expansion side.
If, by contrast, the expansion-side feed chamber likewise extends from a radially outward inlet to a radially inward low-pressure chamber, the working substance on the compression side, when viewed in the radial direction, is fed in the same direction as the working substance on the expansion side. As a result, the inner ends (when viewed in the radial direction) of the spiral strips on the expansion side come to lie approximately opposite the inner ends (likewise viewed in the radial direction) of the compression-side spiral strips in relation to the central disk. The attachment of the inner ends of the spiral strips to the central disk is subjected to high stresses during machine operation and is more or less hot depending on the pressure ratio on the compression side. This arrangement has the advantage that, when such a machine is used at a high compression pressure ratio, heat can be conveyed from the inner hot end of the compression-side strip through the central disk to the cold inner end of the expansion-side strip. This arrangement is of importance when a good heat-conducting light metal is used to produce the displacement body. Use of such light materials results in a relatively low centrifugal force of the displacement component during machine operation.
If the hub of the disk is surrounded by a high-pressure chamber on the compression side, the hub interior is expediently closed off in an airtight manner from this high-pressure chamber by means of a closure piece. By this means, a counterweight, provided to compensate the eccentric movement of the eccentric disk and of the displacement body, can be arranged on the drive shaft advantageously in the expansion-side pressure chamber surrounding the hub. The advantage of such an arrangement is the absolute separation of the lubricant oil from the compressed air.
If the rotor of an electric motor driving the displacement body is arranged on a common drive shaft with the eccentric disk and the displacement body, it is expedient that an intermediate housing is attached to the housing of the electric motor, on that side of the electric motor facing away from the displacement body, into which intermediate housing protrudes the drive shaft provided with a lubricant feed device, and if a housing for a lubricant reservoir is secured on the intermediate housing. Such an arrangement with an intermediate housing is advantageous for receiving, for example, a combined reducing and synchronizing gear system which protrudes into the oil reservoir and is thus lubricated.
If the displacement component is guided in a known manner by a separate second eccentric arrangement, the two eccentric shafts are provided with gearwheels of identical size. These are driven and synchronized by a third gearwheel. The third gearwheel is preferably smaller and sits on the shaft of the drive motor. The latter is designed as a small rapidly rotating electric motor. The weight of the overall compressor/expander unit is thus lower compared with the use of an electric motor rotating at the same speed as the compressor/expander.
It is suitable for the wall of the expansion-side half of the housing to be configured in the area of the outlet in such a way that a container for receiving lubricant is formed together with the outer end of the cylinder wall of the expansion-side feed chamber, said container being connected to the lubricant circuit via external lines. Since the gases leaving the expander have a low temperature, this arrangement of the lubricant oil container at the outer end of the cylinder wall allows the lubricant to cool during machine operation.